Cryo-EM structure of the entire FtsH-HfIKC AAA protease complex

The membrane-bound AAA protease FtsH is the key player controlling protein quality in bacteria. Two single-pass membrane proteins, HfIK and HfIC, interact with FtsH to modulate its proteolytic activity. Here, we present structure of the entire FtsH-HfIKC complex, comprising 12 copies of both HfIK and HfIC, all of which interact reciprocally to form a cage, as well as four FtsH hexamers with periplasmic domains and transmembrane helices enclosed inside the cage and cytoplasmic domains situated at the base of the cage. FtsH K61/D62/S63 in the beta 2-beta 3 loop in the periplasmic domain directly interact with HfIK, contributing to complex formation. Pull-down and in vivo enzymatic activity assays validate the importance of the interacting interface for FtsH-HfIKC complex formation. Structural comparison with the substrate-bound human m-AAA protease AFG3L2 offers implications for the HfIKC cage in modulating substrate access to FtsH. Together, our findings provide a better understanding of FtsH-type AAA protease holoenzyme assembly and regulation.

Automated summary

The membrane-bound AAA protease FtsH plays a crucial role in controlling protein quality in bacteria. In this study, the researchers investigated the structure of the FtsH-HfIKC complex, which includes both HfIK and HfIC proteins. They found that 12 copies of HfIK and HfIC interact reciprocally to form a cage-like structure, with FtsH hexamers enclosed inside. The interaction between FtsH and HfIK was shown to be important for complex formation, and comparison with a human protease provided insights into the role of the HfIKC cage in regulating substrate access to FtsH.